The invention relates to an estimation of the exhaust gas temperature in an internal combustion engine at the outlet of an EGR circuit with which the engine is equipped.
In strategies developed in engine software as regards air management, it is necessary to know the exhaust gas temperature at the outlet of the EGR circuit.
The measurement of the exhaust gas temperature at the outlet of the EGR circuit may be found using a thermocouple measurement.
This solution is precise but expensive (especially due to the cost of the thermocouple and the cost of the acquisition chain). It also requires the provision in the engine compartment of the volume needed to integrate it.
This is why it is becoming increasingly preferable to replace the thermocouple with an estimate of the exhaust gas temperature at the outlet of the EGR circuit.
For this purpose, numerical models based on physics equations are used (e.g. conservation of mass equation and conservation of energy equation).
The major drawback is the lack of precision and reliability of the model.
Specifically, to achieve a high level of precision, it is necessary to solve complex equations involving complex calculation means.
Moreover, these calculation means must be simple enough to be integrated into the computer of the motor vehicle.
An “estimation precision/calculation simplicity” compromise must therefore be found.
Such an approach is conventionally used in calculation means by making assumptions about the physical phenomena governing the exhaust gas heat exchange in EGR circuits and by noting that the exhaust gas temperature drop in an EGR circuit is dependent on the thermal performance of the EGR cooler.
However, trials on vehicles, based on the actual thermal performance of the EGR cooler, have shown that there could be deviations of up to 200 to 300° C. between the estimated and measured gas temperature at the outlet of the EGR circuit.
By numerically adjusting the thermal performance of the cooler so as to attempt to correlate the measurements with the model, the average deviations will thus be reduced to around fifty degrees Celsius.
However, this inaccuracy remains considerable, and therefore unsatisfactory.